Passing argument to array.prototype.findIndex(callback[, thisArg])

I am having trouble passing an argument to the javascript array.prototype.findIndex(callback[, thisArg]) API. The javascript documentation specifies that an argument can be passed but I have not had luck.
This is the API reference Array.prototype.findIndex()

I see this syntax in API:

arr.findIndex(callback[, thisArg])

This is my current implementation but I don't like the way it is implemented with a globally created variable it is not easibly tested code.

I have tried to pass the argument to be used as thisArg in the callback with the following syntax but all resulted in failed attempts. Also I do acknowledge the API mentions the argument will be referenced as this inside the callback, and I have made such adjustment in the callback function.